One of the key benefits of a control system based on the ISA-88 standard is modularity. Modularity begets flexibility. A flexible process control system brings unforeseen benefits throughout its useful lifetime. Even simple systems can benefit from a modular, flexible control system.
Southwest Baking Co. in Tolleson, Ariz., had a problem. The batch system designed for its dough mixers was no longer supported by the OEM that developed and installed it. The bakery had a PC-based batch system connected to Rockwell Automation's control hardware. The PC could fail at any time. With the possibility of a system failure, Southwest Baking needed to do something.
Flexible Dough Mixing
The OEM offered to supply Southwest Baking with a new batch system, which would also be specifically for dough mixing. As an alternative, Southwest Baking turned to Rockwell Automation, supplier of their controller equipment, and ECS Solutions in Evansville, Ind., an RA Authorized Process Integrator and Control System Integrators Association (CSIA)-certified control system integrator. Rockwell Automation's team proposed replacing the OEM batch system with FactoryTalk Batch, which adheres closely to the ISA-88 standard.
FactoryTalk Batch is flexible enough to be applied to any process. However, implementing FactoryTalk Batch carried a higher initial cost than purchasing an upgrade from the OEM. It also raised fear, uncertainty and doubt about modifying the OEM controller code to properly interface with FactoryTalk Batch. This is a smaller system—just the size system which many might say does not need a fully capable batch management system. However, Southwest was able to see the power in flexibility.
"Southwest Baking's upper management fully supports the use of leading edge technology" says Robert Wroblewski, engineering manager at Southwest Baking. "Applying a proven, flexible, off-the-shelf solution that can adapt to our process opens the doors for continuous improvements, even if we don't realize all of the benefits immediately."
FactoryTalk Batch can be applied to any new or existing process in three general steps:
- Determine how you will apply your batch management system (BMS). You must classify your equipment and determine the tasks required to make all your products (Figure 1);
- Determine how you'll either modularize your existing controller code or how you'll replace it with new modular and flexible code; and
- Develop your product recipes.
The first and possibly most critical determination to make is which of the major pieces of process equipment need to be units and which do not. The determining question is, "Does a major processing activity occur inside this equipment?" A pump is not a unit because a pump just transfers material, while the material is unchanged. A raw or finished goods storage vessel is generally not a unit because it's for storage, not processing. ECS determined that four hoppers and the mix bowl filler needed to be defined as units in FactoryTalk Batch (Figure 2).
ISA-88 modularity includes dividing programming that supports what individual pieces of process equipment can do from the programming of how the process equipment will be used.
Programming to make the equipment do whatever it does goes into the basic process control system (BPCS). In this instance, the BPCS was a RA Logix controller system. How the equipment was to be used was "programmed" as FactoryTalk Batch recipes.
The second step ECS took was to make modifications to the BPCS code. ECS kept as much of the OEM programming as possible. The OEM BPCS code was broken up into tasks, each using specific pieces of process equipment. ECS then added logic to interface each task to FactoryTalk Batch.
Jeff Harpenau, the ECS project manager notes, "In hindsight, it would have been more efficient to scrap the OEM code entirely and start over. The code was inflexible and not modular. The wrappers we created to separate the code into phases had to be woven into the existing code, making the changes more challenging." Even Southwest Baking recognized this and asked ECS to evaluate replacing the OEM code entirely with S88 Builder. ECS recommended, and Southwest plans to use, S88 Builder on a potential second line, line one being retrofitted later.